The main difference between using a SRAM crank and a Shimano crank as far as the BB is concerned is that the SRAM setup employs a stepped shim in the left bearing; punch that out of an old GXP BB and you have a HT2 to GXP adapter.
HT2 clamps the whole BB between the cranks, while many GXP cranks just clamp the left bearing with the right side floating, but some GXP cranks use a wave washer on the right, IIRC, effectively clamping the whole BB, which might be necessary if that left bearing is more of a slip fit than a press fit.